Roof drain



Dec. i2, i967 v H. SCHMID ETAL 3,357,561

ROOF' DRAIN Filed Oct. l5, 1965 2 Sheets-Sheet l o 50 /oo R OF 4/7 H Sqft x/ooo JNVENTURS 2m /f Spad BY mav ec. i2, w67 J. H. SCHMID ETAL 3,357,561

ROOF DRAIN 2 Sheets-Sheet 2 Filed Oct. 15, 1965 2 HREH X /000 5@ F72 D'Ql//Y Dow/v 7717.1.- H35.

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n Wmawulmw 1 United States Patent O 3,357,561 RUOF DRAIN John H. Schmid and Norman J. Anderson, Erie, Pa., as-

signors to Zum Industries, Inc., Erie, Pa., a corporation of Pennsylvania Filed Oct. 1S, 1965, Ser. No. 505,108 l Claims. (Cl. 21d-163) This application is a continuation-in-part of application Ser. No. 155,256, tiled Nov. 24, 1961, and now abandoned.

This invention is a drain for dat roofs which controls the rate of run-olf to avoid overtaxing the storm sewer system. The drain offers little resistance to storms of low intensity and increasing resistance to storms of high intensity so that for high intensity storms water will be stored on the roof and a substantial part of the run-olf delayed until after the storm sewer has completed the drainage of surface water. This not only decreases the number of roof drains but also decreases the required size of storm sewers.

The term flat roofs is not limited to roofs which are perfectly flat. Very few roofs are perfectly flat either due t sagging or to variations in thickness of roofing or to intentional pitch. Some roofing contractors deliberately introduce a pitch of from 1/16 to 1A inch per foot (most usually I; inch per foot) toward the roof drains so that the water is always directed toward the roof drains. Other rooting contractors rely upon evaporation to take care of Water which may accumulate in low spots. All of these roofs visually appear to be at and are included within the term dat roofs. Flat roofs with an intentional pitch have less storage capacity than flat roofs without pitch.

In a preferred form, water enters the drain through one or more openings extending above the roof substantially from the minimum to the maximum water level to be accumulated on the roof. The drain openings are widest or of greatest area adjacent the minimum water level and become progressively narrower or of lesser area at higher levels. This holds back the run-off of severe rains and prevents overloading of the storm sewers. In a preferred form, the run-off is controlled by a Weir having a height equal to the maximum water level to be accumulated on the roof and inverted parabolic notches through which the water flows. The capacity of the weir may be varied by selecting the number of notches. In a typical drain, the weir may have from one to six notches, these figures being by way of example rather than limitation. The desired characteristic of the weir is to offer little resistance to run-off of water as water starts to accumulate on the roof and to offer increasing resistance to run-off as the depth of water on the roof builds up. This characteristic is satisiied, for example, by the linear or proportional weir.

In order to select the size of drain required for a flat roof, advantage is taken of Weather Bureau Data such as Rainfall Intensity-Duration-Frequency Curves of the U.S. Department of Commerce Weather Bureau Technical Paper No. 25 which plot for various localities the expected intensity and duration of storms and the frequency or return periods for which such storms may be expected in terms of return periods of 2, 5, 10, 25, 50 and 100 years. By reference to these curves, the expected rainfall for any particular period of time can be determined so that the roof drains can be designed to accommodate the storms.

In the drawing, FIG. 1 is a perspective of a drain, partly broken away; FIG. 2 is a top plan of the Weir; FIG. 3 is a typical set of curves relating the characteristics of the drain to the roof area and the rainfall; FIG. 4 is a diagrammatic view showing the use of the drain on a dat roof; the right hand side showing a roof which is perfectly at and the left hand side showing a roof having an upward pitch or rise from the drain; FIG. 5 is a set of curves for a roof in the same locality as FIG. 3 with a pitch or rise of two inches; and FIG. 6 is a set of curves for a roof in the same locality as FIG. 3 with a pitch or rise of six inches.

The invention is shown applied to a drain having a body 1 with an open top terminating in an outwardly extending clamping flange 2 embedded in the roofing 3. A drain pipe 4 is connected to the lower end of the body. On top of the roofing 3 is the usual clamping collar and gravel stop ring 5 and strainer 6 for keeping gravel and debris out of the drain.

Within the strainer and extending over the top of the body 1 is an annular plate 7 shown here as integral with the clamping collar and having at its central opening an annular Weir comprising an upstanding generally cylindrical wall 8 of height substantially equal to the maximum depth of water to be retained on the roof. The wall 8 is inside or beneath the strainer and is accordingly protected from debris. All of the water entering the drain pipe 4 must pass either through or over the top of the wall 8. From one aspect, the wall 8 is a barrier in the path of flow of the water.

In the wall 8 are one or more notches 9. The lower ends 10 of the notches are positioned at the minimum water level, usually at roof level, although during the summer months extensions may be provided to raise the wall 8 and the minimum level to several inches for cooling purposes. At the lower ends, the notches are wide and oder little or no obstruction to the drainage of water. Light rains drain freely down to the level of the bottoms of the notches. The sides 11 of the notches converge toward each other in an inverted parabolic shape. The notches accordingly loffer progressively greater restriction to drainage as the depth of water accumulating on the roof increases. With the parabolic shape illustrated, the flow through the notches is linearly related to the head of the water rather than as to a higher power of the head as would be true for orifices, The notches 9 offer increasing resistance to the drainage of severe rain and by delaying the run-off prevent overloading of the storm sewers.

The selection of the number of drains to use is illustrated in FIG. 3. Curves 12a, 12b, 12C, 12d, 12e show the height of build-up of water on the roof and maximum drain rate with one drain as a function of the roof area related to the frequency of occurrence of severe rains. The storms of extreme severity which occur only once every hundred years are indicated by the curve 12a which is also labeled 100. The curves 12b to 12e for storms of lesser severity which occur more frequently are similarly labeled in accordance with the frequency of occurrence. For example, in the locality covered by FIG. 3, if the maximum depth of build-up of water on the roof is to be held to a maximum three inches for storms of severity occurring every ten years, one drain would be required for each 10,080 square feet of roof. This is less than one-third the number of roof drains which would be required by the National Plumbing Code ASA 40.8 method. Curves 13a, 13b, 13C, 13d, 13e, 13j, 13g, 13h, 131', show the time required to drain water from the roof as a function of roof area and depth of accumulated water. For the roof area of 10,080 square feet with accumulated water at the three inch level, the maximum discharge rate to the drain pipe would be gallons per minute and the time required to drain the roof would be about 3% hours.

FIG. 3 also shows what would happen for storms of greater severity. The once in 25 year storm will build up to 3.6 inches depth on the roof and drain at the rate of 215 gallons per minute while the once in 100 years storm will build up to a head of 4.4 inches and drain at a maximum of 265 gallons per minute. This provides the data needed to select the most suitable storm sewers. If no ooding `can be tolerated, the storm sewers will have to be sized to take care of the most severe storms while if the effect of ooding is not serious, smaller storm sewers can be used. The size of storm sewers will always be smaller than required by drains having unrestricted run-off.

By having the run-off relatively unrestricted at low levels and with increasing restriction as the level increases, more effective use is made of the drains. The relatively unrestricted run-off at low levels retards the build-up of water on the roof. That is, it takes longer to reach the maximum level. The linearrelation between the run-olf and the water level also simplifies the calculations needed to size the drains.

Upon reachhig the maximum level for which the drain is designed, the water spills over the upper edge of the wall 8 and drains freely. From one aspect, above the maximum water level, the restriction to ow no longer increases within increasing height but decreases.

In `order to reinforce the wall 8, external ribs 1S are provided on the sections 16 between the notches 9 and the upper ends of the sections 16 are connected by a spider 17. The ribs and spider are for structural strength and do not effect the characteristics of the drain.

If the Weir 8, 9 were omitted, the gravel stop ring 5 would restrict the run-off, but in a non-linear manner with resultant difficulty of calculation and design. In the present drain, the restriction offered by the ring is less than that offered by the weir 8, 9 so the run-off is controlled solely by the Weir.

FIGS. 5 and 6 are curves for the same area as FIG. 3 for Hat roofs with intentional pitch, FIG. 5 being for a rise of two inches from the drain to the edge of the roof and FIG. y6 being for a rise of six inches. FIGS. 5 and 6 are for drains having a Weir with a single notch while FIG. 3 is for a drain with a Weir having six notches. Stated differently, the drain for the curves of FIGS. 5 and 6 has one sixth the capacity of the drain for the curves of FIG. 3.

As illustrated in FIG. 4, the rise of the flat roof reduces the storage capacity. At the right hand side of FIG. 4 the upper surface 18 of the roof is ilat and the depth of water adjacent the drain is the same as adjacent the outside wall 19 which may be provided with the usual overflow 20. At the left hand side of FIG. 4, the depth of water adjacent the outside wall 21 is less than the depth adjacent the drain by an amount equal to the rise This subtracts from the roof storage capacity and enables each drain to take care of less roof area. For example, referring to FIG. 5 where curves 22a, 22b, 22C, 22d, 22e show the height of maximum build-up of water at the drain for storms of severity occurring once in 100, 50, 25, l0 and 5 years respectively,.it will be noted that for curve 22h (corresponding to curve 12b) each notch in the Weir will accommodate 975 square Ifeet of roof for a build-up 0f 31/2 inches in a storm of such intensity as to be expected only once every 50 years. According to curve 12b, the same build-up in water level would occur with a roof area of 7200 square feet, 1200 square feet of roof area per notch. Similarly, in FIG. 6 where curves 23a, 2311, 23C, 23d and 23e show the height of maximum build-up of water at the drain for storms of severity occurring once in 100, 50, 25, and 5 years respectively, it will be noted that for curve 23b (corresponding to curve 12b) that each notch in the weir will accommodate 650I square feet of roof area for a build-up of 3% inches in a storm of such intensity as to be expected only once every 50 years. To take care of the same roof area, drains for roofs with pitch or rise require greater height. For curves 22]) and 23h and a roof area of 4 1200 square feet (the same roof area accommodated by each notch in FIGS. 1 3), the build-up of water at the drain during the 50 year storm would be 3.8 inches and 4.8 inches respectively. Even if the depth of build-up of water is increased to take care of the pitch or rise, there is a faster drain down as shown by curves 241mc and 25a-k. The build-up of 3.8 inches for the 50 year storm requires only slightly more than two hours to drain down for the roof with two inches rise while the build-up of 4.8 inches requires only one hour to drain down for the roof with the six inch rise. This should be compared with the 21/2 hour drain down time for the comparable flat roof with no pitch or rise. For flat roofs with pitch or rise, the height of the strainer and Weir should be increased to take care of the increased depth of water build-up at the drain and the size of the drain pipes should also be increased to take care of the increased speed of run-off. However, the advantages obtained are of the same kind as withroofs which are perfectly lat.

The linear or proportional Weir greatly simplifies the calculations required to correlate the storm data with roof area. For one such Weir, the ilow characteristics are expressed by the equation Q=l.603h. Then for the perfectly at roof, the time required for the water load to build up to a given depth is given by the equation:

t* ai.) L 1.603 Anrfi-1.60m

The drain down time is given by the equation:

where the symbols have the same meaning. The logarithmic form of the equation simplifies the correlation withv the storm data which is also available in logarithmic form. The linear or proportional weir is not limited to the parabolic notch. Such weirs have the characteristic of greater area at low heads with lesser area at higher heads, a characteristic of the parabolic notch. Other linear flow control devices which are not weirs are known. Regardless of the type of ow control device selected, it should offer less restriction at low levels and increasing restriction at higher levels to provide free run-olf for light storms and retarded run-olf for heavy storms.

A substantially linear relation between hydraulic head and flow is an important advantage in correlating the roof area and storm data to the drains. When the relation be tween hydraulic head and flow is non-linear, the calculations become too complex, both to compute and to put the results in usable form, to be practical. The linear relation to flow made possible the correlation of the storm data and the roof drains so an engineer can now select the correct number of drains for a given iiat roof in a given locality and know the maximum depth of water that will accumulate on the roof, the flow rate to the storm sewer, and the drain down time after the storm abates under the storm conditions that will be experienced in the given area. Such data has never been available until the concept of a linear ow drain system.

Proportional ow drainage is not limited to dead Hat roofs such as the curves in FIG. 3 apply to. The use of drains which discharge at a rate directly proportional to the hydraulic head on the drain also makes it possible to predict water depth, ilow rate, and drain down time for sloping or pitched roofs. The calculations for this condition are more complex than for a flat roof as the storage volume, in relation to water depth, changes as the water depth exceeds the rise of the roof. With sloping roofs, curves can be established for any locality for roofs having a given rise. FIGURES and 6 show curves for roofs having 2 and 6 rise respectively for the same locality as represented by EEIG. 3. These permit the engineer to select the correct number of drains and predict water depth on the roof, discharge rate and drain down time for the roof rise he designs into the building. In this type of construction, as in the case of flat roofs, the proportional Weir makes possible the calculation and recording of data in useable form which has not been possible before the design of a roof drain with a proportional weir.

What is claimed as new is:

1. A roof drain comprising a body having an open top and a discharge at its lower end for connection to a drain pipe, a dome strainer extending over the top of the body for keeping debris out of the drains, a ow control means beneath the strainer and having an upstanding wall between the strainer and the discharge through which water must ow, and said wall having at least one notch having sides defined by inverted parabolic curves with its wider end adapted to be positioned at and form the minimum water level and said notch having sides converging toward each other at higher levels to oer progressively greater restriction to drainage as the water level increases.

2. A roof drain comprising a body having an open top and a discharge at its lower end for connection to a drain pipe, a dome strainer extending over the top 'of the body for keeping debris out of the drains, a plate beneath the strainer and above the discharge and having its peripheral edge secured to the body, an upstanding wall between the strainer and the discharge at the center of the plate through which water must ow, and said wall having at least one notch having sides widely separated at the lower end with its wider end adapted to be positioned at and form the minimum water level to oier relatively little restriction to drainage of water at the level of the lower end of the notch and the sides of the notch being progressively less widely separated toward the top to oier greater restriction to drainage as the water level rises, said wall being proportioned to have a ow rate substantially equal to a constant times the head of water above said minimum water level.

3. In combination with a flat roof elevated at its periphery to retain water on the rooi:` and dening a water level equal to or greater than the maximum water level to be stored on the roof, a drain within the periphery of the roof comprising a body having a discharge at its lower end for connection to a drain pipe, ilow control means having a weir above the discharge and discharging to the lower end of the body, the height of the weir being substantially the maximum water level, and the weir having at least one notch with sides Widely separated at the lower end of the notch and progressively less widely separated toward the top of the notch to offer progressively greater restriction to drainage as the water level increases and with its wider end adapted to be positioned at and form the minimum water level, said Weir being proportioned to have a iiow rate substantially equal to a constant times the head of water above said minimum water level.

4. In combination with a liat roof elevated at its periphery to retain water on the roof and deining a water level equal to or greater than the maximum water level to be stored on the roof, a drain within the periphery of the roof comprising a body having a discharge at its lower end for connection to a drain pipe, flow control means having a barrier above the discharge in the path of the ow of water to the discharge and having its lower end discharging to the lower end of the body, said barrier being adapted to be positioned with its lower end at a minimum water level and with its upper end projecting substantially to the maximum Water level, and said barrier having at least one opening in its side between its upper and lower ends and proportioned to have a flow rate through said opening substantially equal to a constant times the head of water above said minimum water level.

5. In combination with a flat roof elevated at its periphery to retain water on the roof and defining a water level equal to or greater than the maximum water level 'to be stored on the roof, a drain within the periphery of the roof comprising a stand pipe having a lower end for connection to a drain pipe and sides upstanding to substantially the maximum level of water to be retained on the roof, said sides being perforated to permit ow of water into the stand pipe, the area of perforation varying between the minimum and maximum water levels being least at the maximum water level and progressively greater toward the minimum water level to offer less resistance to ow at low levels and increasing resistance to ow at high levels, said stand pipe being proportioned to have a flow rate substantially equal to a constant times the head of water above said minimum water level.

6. The combination of claim 5 in which the roof has a pitch or rise upward from the drain toward the peripheral walls.

7. In combination with a nominally dat roof designed to retain water on the roof and defining a water level equal to or greater than the maximum water level to be stored on the roof, a drain having a body positioned within the periphery of the roof and having a discharge at its lower end for connection to a drain pipe, said body having a iiow control means responsive to the head of water on the roof above a minimum level and positioned in the path of the llow to said discharge, said ilow control means having a ow rate substantially equal to a constant times the hydraulic headV of water above said minimum level.

References Cited UNITED STATES PATENTS 1,067,491 7/1913 Simmance et al. 73-215 1,080,052 12/1913 Englebright 73-215 X 1,138,700 5/1915 Sutro 73--215 1,180,018 4/1916 Degnan 210-163 1,973,321 9/1934 Schultz 210-163 2,283,160 5/1942 Boosey 210-163 2,572,208 10/1951 Sievert 210-166 2,666,493 l/1954 Gordon 210`166 SAMIH N. ZAHARNA, Primary Examiner.

REUBEN FRIEDMAN, Examiner.

F. W. MEDLEY, Assistant Examiner. 

2. A ROOF DRAIN COMPRISING A BODY HAVING AN OPEN TOP AND A DISCHARGE AT ITS LOWER END FOR CONNECTION TO A DRAIN PIPE, A DOME STRAINER EXTENDING OVER THE TOP OF THE BODY FOR KEEPING DEBRIS OUT OF THE DRAINS, A PLATE BENEATH THE STRAINER AND ABOVE THE DISCHARGE AND HAVING ITS PERIPHERAL EDGE SECURED TO THE BODY, AN UPSTANDING WALL BETWEEN THE STRAINER AND THE DISCHARGE AT THE CENTER OF THE PLATE THROUGH WHICH WATER MUST FLOW, AND SAID WALL HAVING AT LEAST ONE NOTCH HAVING SIDES WIDELY SEPARATED AT THE LOWER END WITH ITS WIDER END ADAPTED TO BE POSITIONED AT AND FORM THE MINIMUM WATER LEVEL TO OFFER RELATIVELY LITTLE RESTRICTION TO DRAINAGE OF WATER AT THE LEVEL OF THE LOWER END OF THE NOTCH AND THE SIDES OF THE NOTCH BEING PROGRESSIVELY LESS WIDELY SEPARATED TOWARD THE TOP TO OFFER GREATER RESTRICTION TO DRAINAGE AS THE WATER LEVEL RISES, SAID WALL BEING PROPORTIONED TO HAVE A FLOW RATE SUBSTANTIALLY EQUAL TO A CONSTANT TIMES THE HEAD OF WATER ABOVE SAID MINIMUM WATER LEVEL. 